EP 1 509 353 B1 discloses a cutting insert for milling square shoulders of the type defined in the introduction. An advantage of this insert with respect to other known inserts being curved at the side surfaces provided with opposing major cutting edges and for that sake having curved support surfaces is that the two generally flat and non-coplanar support surfaces will press against larger faces on an insert pocket. This means that the insert will be more stable in the insert pocket than would only a small part of the insert press against faces or even points of the pocket as for a curved design. The two support surfaces, which will form radial supports, of the insert disclosed in this publication make different angles with a normal to the bottom surfaces of the insert for trying to consider forces acting on cutting edges thereof when determining the radial support to be provided through the respective support surface. Although this cutting insert has favourable features there is of course an ongoing attempt to improve the properties of an insert of this type, especially with respect to a combination of stable support in an insert pocket of a milling cutting tool and long lifetime of the insert.